Postmastectomy Scar Boost Irradiation Using HDR Surface Mould Brachytherapy by 3D Image-Based Volume Optimization

Abstract

Introduction: During postmastectomy radiotherapy (PMRT), it is recommended to boost the postmastectomy surgical scar with additional 10 Gy in 5 fractions in the patients with close or positive surgical margins. The electron beam therapy, though cumbersome, is usually preferred since it has the desired rapid fall of a dose beyond R 85 . An alternative but easier and reproducible treatment method for PMRT surgical scar boost using 3D CT image-based HDR surface mould brachytherapy is introduced and analyses of the target coverage and dose nearby organs-at-risk (OARs) using this method are evaluated in this study. Methods and Materials: This study includes twelve patients (five left-sided and seven right-sided chest wall), who were planned and treated with CT-image based surface mould HDR brachytherapy for chest wall scar boost (CWB) using Catheter Flap Set TM (Varian Medical Systems, USA) that were given concurrently during external beam radiotherapy (EBRT) treatments. Since no guidelines are available for delineating clinical target volume (CTV) structure to be used for postmastectomy scar boost, the CTV in this study was a uniform 5-mm thick volume drawn at 5 mm beneath the skin (CTVhdr_evl) and its extent was made conforming to the boost area marked on the skin and made visible in CT images by radiopaque wires. Results: Prescribed dose (PD) to CTVhdr_evl is 7.5 Gy in 3 fractions, and 2.5 Gy per fraction. The CTVhdr_evl volume receives the PD with mean V 100% , V 98% and V 95% values which are 98.57%, 99.63% and 100% respectively. The mean dose for heart (MHD) is 2.71 Gy in left-sided CWB and 1.80 Gy in right-sided CWB plans. Mean lung dose (MLD) is 2.48 Gy for ipsilateral lung and 0.76 Gy for contralateral lung. Maximum dose to contralateral breast is 4.93 Gy and the mean dose is 0.79 Gy. The mean percent dose to the skin volume overlying the CTVhdr_evl is 138.6% and 3.7% of skin volume received 200% of the PD. Conclusion: The 3D image-based HDR surface mould achieved good CTV coverage with acceptable doses to OARs. Patient preparation, treatment planning, and execution in this method are less cumbersome and reproducible. Thus surface mould using flap applicator can be used whenever postmastectomy surgical scar boost is required.

Impact of GBBS algorithm on post-mastectomy scar boost irradiation of breast using catheter flap

“…A difference of -3.7% was observed in the Acuros ® BV calculation to the prescribed dose. These results are comparable with mean cardiac doses reported by a similar study (D mean of 0.9 Gy with TG-43 dosimetry) [7]. The dose receiving a 2.0% volume was 129.4 cGy with standard calculation and 122.02 cGy with Acuros ® BV-based dosimetry, -5.7% decrease was noted comparing with the current dosimetry technique.…”

“…The advantages of brachytherapy over electrons are a rapid dose fall-off outside the target volume and short treatment duration [6]. There is an extreme lack of studies investigating the role of HDR surface mould brachyther-apy scar boost following PMRT, in the setting of close or positive margins [7]. Our experience over many trials in designing the standard mould for scar boost irradiation and air gaps leads to inhomogeneity in dose.…”

Post-Mastectomy External Beam Radiation Followed by HDR Surface Mould Brachytherapy Boost vs. External Beam Radiotherapy Alone in High-Risk Casesa Randomised Controlled Trial

“…It was first described by Vijayaprabhu et al in a single arm pilot study. [15] This protocol is not complicated with use of electron arc and electron beam techniques. Chest being a curve structure and due to presence of lung, bone and soft tissue heterogeneities, a great challenge is being faced for planning of irradiation.…”

“…There is extreme paucity of studies investigating role of HDR surface mould brachytherapy scar boost following PMRT in the setting of close or positive margins except one study from India. [15] But it was basically a pilot study and not a randomised trial comparing brachytherapy boost with control arm. So, in this study we have attempted to compare PMRT followed by brachytherapy boost in the study arm with the control arm treated with PMRT alone in close or positive margin cases in a randomised trial.…”

An alternative option to reduce lung dose for electron scar boost irradiation in post-mastectomy breast cancer patients with a thin chest wall

“…2,4 The most common treatment planning technique is opposed tangential megavoltage photon fields for the CW and an en face electron field for the scar boost. 2 While various treatment planning options such as electron beam only, combined photonelectron beams, proton therapy, intensity modulated radiation therapy or volumetric modulated radiation therapy have been used for CW irradiation, [5][6][7][8][9][10] the electron beam therapy is still the most common and preferred technique for scar boost irradiation because of the simplicity of treatment and the easy setups, 11 despite the availability of simultaneous integrated boost or high-dose rate treatments. 4,11 However, one of the disadvantages of this en face electron field treatment technique is the radiation dose delivered to the underlying normal lungs, which can result in acute radiation induced toxicity such as radiation pneumonitis (RP).…”